How much water does your roof put next to your wall?
This is usually the largest single water source acting on a foundation, and the cheapest one to redirect. The number surprises people.
The arithmetic nobody does before spending five figures inside. This is usually the largest single water source acting on a foundation, and the cheapest one to move.
The arithmetic, so you can check it
One inch of rain on one square foot is 0.623 US gallons. So roof footprint × inches of rain × 0.623 gives total gallons, and dividing by the number of downspouts gives what each one delivers. Nothing here is controversial — it is just arithmetic almost nobody does before spending $15,000 on interior drainage.
What good discharge looks like
Ten feet from the wall as a minimum, further on clay.
Downhill from the point of discharge, not into a flat spot that becomes a pond.
Not into a neighbour’s yard, which is a legal problem in most states, and not into a sanitary sewer, which is illegal in most municipalities and can back sewage into your own basement.
If buried: rigid smooth-wall pipe with a cleanout, not corrugated flexible pipe, which silts up and cannot be cleared.
Freeze path considered, in every state we cover except the southern edge.